1. Field of the Invention
The present invention relates to a radio wave receiving device with a magnetic drive unit and an antenna structure, and an electronic apparatus using the radio wave receiving device.
2. Description of the Related Art
As a radio wave receiving device with a magnetic drive unit and an antenna structure, a time piece module incorporated in so-called radio wave controlled time piece can be exemplified.
The radio wave controlled time piece has been already known and is configured to receive standard radio wave containing time information so as to automatically correct a current time. The radio wave controlled time piece includes a time piece case including an accommodation space at least a part of which is opened, a time piece module accommodated in the accommodation space of the time piece case through the opening, a light transmission lid which covers the opening, a partition panel disposed in the accommodation space of the time piece case so as to partition the accommodation space between the time piece module and the light transmission lid, and at least one time indicating hand which is disposed between the light transmission lid and the partition panel within the accommodation space of the time piece case and driven by the time piece module to indicate a time on the partition panel.
The time piece module is one kind of electronic apparatuses, and includes a radio wave receiving device including a motor for driving the at least one time indicating hand and an antenna structure for receiving the standard radio wave including time information. The time piece module further includes an operation control circuit part which controls the operation of the motor so as to make the at least one time indicating hand indicate a current time on the partition panel and which drives the motor based on the time information contained in the standard radio wave received by the antenna structure so as to correct the current time indicated by the time indicating hand on the partition panel. Then, the motor is one kind of magnetic drive unit which is driven by magnetic force.
The antenna structure includes a narrow core formed of magnetic material such as amorphous metal, ferrite, permalloy and the like, and a coil wound around the central portion of the core.
The motor for the time piece module is required to be operated at a high precision and the antenna structure is required to have a high receiving sensitivity. To prevent the operation of the motor from being affected by external magnetic field, the time piece module is so configured that a side facing to the opening and the other side being opposite to the opening are covered with antimagnetic plates in the accommodation space of the time piece case because magnetic flux of the external magnetic field can enters into the accommodation space of the time piece case easily through the opening and its side opposing to the opening.
However, the antimagnetic plates reduce the receiving sensitivity of the antenna structure.
A structure which not only can guarantee the accuracy of the operation of the motor but also prevents the receiving sensitivity of the antenna structure from being lowered in the time piece module having the antimagnetic plates has been disclosed in, for example, Japanese Patent Application KOKAI Publication No. 2004-294258.
In this conventional structure, openings are formed in portions of the antimagnetic plates corresponding to the coil of the antenna structure of the time piece module.
The above-described conventional structure can prevent the receiving sensitivity of the antenna structure from lowering to some extent by using the antimagnetic plates, but a further improvement has been demanded.
The present invention has been derived under the above-described circumstances, and an object of the invention is to provide a radio wave receiving device with a magnetic drive unit and an antenna structure, which is capable of guaranteeing the precision of the operation of the magnetic drive unit against external magnetism and improving the receiving sensitivity of the antenna structure greatly more than conventional one.